In this specification, where a document, act or item of knowledge is referred to or discussed, this reference or discussion is not an admission that the document, act or item of knowledge or any combination thereof was at the priority date:    (i) part of common general knowledge; or    (ii) known to be relevant to an attempt to solve any problem with which this specification is concerned.
Fire fighting buckets carried by an aircraft such as a helicopter are well-known, and have been used with success in controlling fires in many countries including Australia, the United States and Canada.
In general, a bucket of this nature is suspendible from a helicopter by a sling or harness and, by virtue of its open-topped and closed bottom construction, is capable of being filled with water from an available water source such as a lake, dam, river or ocean by the lowering of the bucket into the water source. When filled, the bucket is raised and the pilot transports the bucket to the site of the fire, following which the water is discharged onto the fire by remote activation by the pilot of a valve in or near the region of the base of the bucket.
Typical examples of such buckets can be found in the disclosures in U.S. Pat. Nos. 3,661,211, 4,474,245, 4,576,287 and 5,560,429.
U.S. Pat. No. 3,661,211 for example discloses a flexible open-topped bucket having a pair of pneumatic-ram operated doors which open upwardly to release the contents of the bucket. The ram-operated doors are in the form of a ‘plunger-type’ valve or ‘gate’ valve operated by a fluid-operated ram connected to a pressurized fluid source in the helicopter.
Because the valves are typically hydraulically or electrically actuated, they are heavy and prone to failure. The nature of this arrangement is also such that it is capable of only a single water drop, which only enables a fixed amount of water to be dumped on the fire, and necessitates more frequent returns by the pilot to the water source to refill the bucket.
If a fire is raging in a remote location with restricted or no access to a readily available source of water, this will naturally increase the number of trips the pilot has to make back and forth from the fire to the water source.
This can severely impact on the effectiveness of this fire-fighting technique, and also increases the cost of the helicopter being in the air, the potential risk to the pilot through fatigue, the possibility of equipment failure, greater use of fuel and so on.
It will be understood that dumping a fixed amount of water on a fire which may only require a fraction of the fixed amount in order to be effective, is an inefficient use of this resource, and may lead to a different but no less harmful type of damage to the environment.
The disclosures in U.S. Pat. Nos. 4,474,245, 4,576,287 and 5,560,429 describe a flexible bucket where the ‘plunger-type’ valve is replaced with a ‘sleeve-type’ dump valve. A tubular extension made of the same pliable material as the bucket extends from an opening in the bottom of the bucket to a free end formed with a discharge port to serve as a dump valve. The discharge port has a circumferential sealing lip made of soft resilient material which forms two opposite lip portions that are brought into sealing engagement with each other to minimize water leakage from the tubular extension when the sleeve is held raised within the bucket.
To dump the water, the sleeve is released by loosening purse lines by a release mechanism, causing the sleeve to fall quickly through the opening in the bottom of the bucket. The lip portions are opened simultaneously under the weight of the water, permitting a rapid discharge of the water. This type of bucket arrangement is typically referred to in the industry as a Bambi Bucket™.
Although buckets of that configuration are said to have been very successful, the sleeve-type dump valve is a single action valve whereby the bucket releases all of its load in a single discharge. Accordingly, it cannot be closed during discharge to allow for a second discharge at a remote location. This again leads to inefficient use of water and helicopter time, necessitating more frequent visits to the water source to fill the bucket.
In addition, the relatively soft sealing material of the lip portions of the discharge port can wear rapidly after many deployments of the valve due to the abrasion of the purse lines. The wear is likely to result in loss of sealing effectiveness and resultant leakage through the dump valve.
One attempt at addressing this problem is disclosed in U.S. Pat. No. 5,829,809, which is said to permit the discharge of two separate loads from a single filling of the bucket by having an outer bucket with an outer sleeve-type dump valve and an inner bucket with an inner sleeve-type dump valve, the inner bucket being located within the outer bucket.
Such an arrangement is however likely to suffer from ineffective filling of both buckets because the inner bucket rests inside the outer bucket. In addition, as observed above, the relatively soft sealing material of the lip portions of the discharge port can wear rapidly after many deployments of the valve due to the abrasion of the purse lines. The wear is likely to result in loss of sealing effectiveness and resultant leakage through the dump valve.
There is also some risk of tangling of the purse lines.
A further problem with prior art buckets described above is that the bucket load can only be controlled manually by means of a cinch strap. This strap passes circumferentially around a portion of the bucket approximately midway and passes through a plurality of loops provided on the inner surface of the side wall. The load in the bucket is controlled by varying the tightness of the strap. This requires the helicopter pilot to land the helicopter and tighten or loosen the cinch strap manually. It is time consuming, and necessitates the pilot having to find suitable terrain on which to land, leading to increased risk to the pilot.
Zipper or slide fasteners in the side walls of the bucket in order to control the magnitude of the load being carried have been proposed as an alternative to the cinch strap—see for example U.S. Pat. No. 3,661,211. Zipper fasteners however suffer from the same disadvantage as cinch straps—they require the pilot to engage in a manual manipulation of the fasteners on the ground.
U.S. Pat. No. 6,192,990 discloses a valve which is said to permit the discharge of multiple separate loads from a single filling of the bucket. The valve comprises an inner assembly of a top plate and a bottom plate and an outer assembly of a solid side wall that forms a cylinder shape with the top and bottom plates. When the valve is in a dosed position, respective upper and lower portions of the side wall make a sealing engagement with the top and bottom plates. The valve is opened by moving the side wall in an upwards direction away from the plates, with the water flowing into the open sides of the valve and out of an opening in the bottom plate. Similarly, the valve is dosed by moving the side wall back into sealing engagement with the top and bottom plates. The valve can be dosed before the bucket is emptied to permit the discharge of multiple loads.
Upwards movement of the side wall is achieved by a mechanical actuator that is controlled by the helicopter pilot from the cockpit. Downward movement of the sidewall may also be provided by the mechanical actuator, as well as by the weight of the water in the bucket and/or other means such as a tension spring. The valve may also be partially opened to control the rate of flow from the bucket by varying the distance of movement of the side wall away from the top and bottom plates, which may be monitored by position sensors.
The valve of U.S. Pat. No. 6,192,990 suffers from a number of disadvantages. Principally, it requires a heavy and expensive motorised actuator to open the valve.